I've had really good luck with the battery polaris uses! my two old rangers I never replaced the batteries in at all before I traded them off. They were 5 and 6 years old!
The 800s I haven't has as good of luck with, one ranger still has the original battery, the the other two have had their battery replaced with a Deka brand batt. So far so good.
I've had Gel batteries for my vehicles, they aren't worth the money. Never had one last over 3 years, with most of them failing after 2 or 3.
Had one optima red top that was replaced 4 times before I said screw it and bought an interstate...
Most lead acid batteries will be traded off with their machines long before you need to do any maintenance to them.